Dave, On Feb 5, 2007, at 8:35 PM, Dave Perry wrote: > Hi Tat, > > Thanks for this great addition! > > I took a look at the j7w Shindon including the j7w.xml yasim > configuration. Did you know there is a command line yasim in > $FG_ROOT/bin that allows you to get a lot of feedback from a trial > config xml file like j7w.xml w/o running fgfs?
Thanks for the xml file. It's a great help. Yes, I know there's a command line version of yasim but didn't try it since I use Mac version of FlightGear and it doesn't come with the command line yasim unfortunately. # Oh, I'm the one who develops the Mac version so this misfortune is made by myself :-p > After a flight in the > Shindon, I was fairly certain that the CG (center of gravity) was too > far forward. This required you to use an effectiveness of 3.5 on the > cannard. And you did get the desired increase in stability. So I > made > an estimate from the 3D model as to approximately where the CG should > be. The main wing should cary most of the weight, so since the > wing is > swept, I tried to change the ballast to move the CG to about x = > -1.7 m > (yours is at x = -0.666), or approximately at the leading edge root. > This allowed me to reduce the cannard effectiveness to 1.5. I gave it a try and your configuration file seems very close to what I want. It's a great help. I was about to calculate the CG and some other parameters with a bit more engineering way so I looked more deeply into the flight model but hard to find the way to see the CG in yasim. your post saved me a lot! Plus, taking a look at your xml file told me that I mistakenly settled the position of the main gears. It should be -2.15 instead of -1.64 so your guess is right. And the biggest mystery in my head was resolved. I calculated the position of CG with the equation obtained at: http://www.paragonair.com/public/docs/FAA-Handbooks/8083-01_WnB/ 8083-01_ch08.pdf According to this document, the distance from the nose to the CG is calculated as: CGoffset = D - (F*L) / W where D is the distance between the front wheel and the main wheel, F is the weight of the front wheel, L is the distance between the nose and the main wheel, and W is the total weight of the aircraft. I estimated the weight of the front wheel as 1/6 - 1/8 of the total weight. Then the CG is placed between 6.43 to 6.59 m behind the nose. The nose is at 4.89 m in x-axis so the position of the CG can be between -1.54 and -1.70 on x-axis. I'm now trying the actual weight of Shinden (I was using the lighter weight since Shinden was not stable at all) I tried various CG point in between the positions above. -1.54 seems a little bit front heavy and 1.70 looks just a little bit rear heavy with the accurate mass since reseting flightgear lifts the nose up. > Also, from > your data, I see that the power off dirty stall is 67 knots, so I used > that in the approach configuration (yasim assumes that the approach > speed is the dirty stall speed). This allows a slower stall and > better > short field landings with approach at 85 knots. I flew from KSFO to > KHLF and landed and turned off before the tower with little braking. 67 kts for the dirty stall is for A6M2 (sorry, I forgot to delete these). The one for Shinden should be a bit faster (probably around 75 - 85) since its flight record says it landed at 100 or 120 kts. I'm not pretty sure if it actually stall at this speed because there's no such record as far as I know. (67 is very tempting parameter to me though.) By the way, the record says that it needed to put the elevator all the way down at the full-flap to avoid the nose going down. so the approach elevator in command-line yasim should be more than 0.9, I guess. With a couple of test flights using the revised j7w.xml, I landed Shinden at about 100 kts with three point landing with full-flap, and 90 kts with a little bit aerodynamic landing (maybe I was lucky). Anyway, I updated the files at: http://http://macflightgear.sourceforge.net/home/aircraft/j7w There're several other improvements such as engine power, flap-driven elevator trim control, etc. plus sweep angle, mass of both aircraft and engine, wheel positions are corrected. I'm going to try proptest to see how to adjust the engine/prop configuration Again, thanks for making your effort on this. I really appreciate it. Martin, could you download the diff file from the link above and commit it for me? Please commit with the comments that includes the revision history written at 20070205 and 2070206 in the Revision History section. Tat ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier. Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
